Some of the world’s richest people – including Warren Buffett, Mark Zuckerberg and Jeff Bezos – lost billions apiece on Monday as stocks took an ugly nosedive.

The Dow Jones Industrial Average plunged 1,175 points, or 4.6%, marking the largest one-day drop the blue-chip index has ever seen and wiping out its gains for the year. The Dow, which tracks 30 U.S. companies, is now down 2% so far this year. The S&P 500 and Nasdaq also fell by about 4% each on Monday.

Warren Buffett was hit the hardest by the sell-off: The drop shaved $5.3 billion off his net worth – a nearly 6% drop in just one day. He is still the third-richest person in the world with a net worth of $84.6 billion, according to Forbes real-time billionaire rankings.

Facebook CEO Mark Zuckerberg was next in line, shedding $3.6 billion, or 4.7% of his net worth, as shares of his social media company dropped 5%. He finished the day with $73.1 billion to his name.

Amazon’s Jeff Bezos, the richest person on the planet, saw his fortune drop $3.2 billion. That erases the $3.2 billion he gained one day last week after his company announced blockbuster quarterly results. He is still worth an astounding $115.7 billion, which puts him $25 billion ahead of the second-richest person on the planet, Microsoft cofounder Bill Gates.

Altogether, the six billionaires that suffered the most from the market rout saw their fortunes shrivel by a whopping $18.8 billion in a single day. Many of the world’s richest people have their net worth tied up in shares of their publicly-traded companies and are vulnerable to fluctuations in the market.

To be sure, these billionaires have benefited hugely from a relentless bull market that is coming up on its nine-year anniversary. The S&P 500 gained 19% in 2017, driven in part by record corporate profits and an improving economy. Jeff Bezos, for instance, has become $28 billion richer in just the last four months as shares of Amazon rose 30%. – Written by Lauren Gensler, FORBES STAFF